Table 1.

Summary of MTX and pemetrexed influx kinetic values for wild-type and G338C mutant PCFT

				Vmax, pmol•mg protein•−1min−1
	Kt , μM	Mutant/Wild-Type	Ki, μM	Uncorrected	Relative expression at the cell surface (G338C/wild-type)	Corrected for expression	Mutant/wild-type; corrected for expression
Wild type
MTX	3.37 ± 1.09		2.3 ± 0.3	571.0 ± 76.4	1.0
PMX	0.59 ± 0.21		0.18 ± 0.04	147.6 ± 17.5
G338C
MTX	0.17 ± 0.05	0.05	1.1 ± 0.3	7.85 ± 0.53	0.73	10.7	0.02
PMX	0.04 ± 0.02	0.07	0.12 ± 0.02	7.65 ± 0.55		10.5	0.07

Values are means ± SE. A comparison of methotrexate (MTX) and pemetrexed (PMX) influx kinetics based on the experimental data of Figs. 3, 4, and 5. Relative expression was measured by ImageJ densitometry in two separate experiments and was used to normalize V_max. The P values for differences between the K_t (concentration of substrate at which influx is half the maximum rate of transport) and K_i (inhibition constant) for wild-type proton-coupled folate transporter (PCFT) were 0.08 for pemetrexed and 0.09 for MTX. The P values for differences between the K_t and K_i for the G338C-PCFT mutant for pemetrexed was 0.001 and for MTX was 0.03.